


Miscalculation

by entermate



Category: Undertale (Video Game)
Genre: Alternate Universe - Handplates (Undertale), Ecto-Genitalia (Undertale), Ecto-Penis (Undertale), Ecto-Tongue (Undertale), Ecto-Vagina (Undertale), M/M, Mating Bites, Mating Cycles/In Heat, Mildly Dubious Consent, Smut, Underage Sex, no beta we die like men, the Dubious Ethics that comes standard in Handplates
Language: English
Status: Completed
Published: 2019-01-02
Updated: 2019-01-02
Packaged: 2019-10-02 20:37:35
Rating: Explicit
Warnings: Underage
Chapters: 1
Words: 2,794
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/17270726
Author URL: https://archiveofourown.org/users/entermate/pseuds/entermate
Summary: 2-P made a noise of discontent, leaning further on his brother's side, reveling in the feeling of cool bones against his own. He felthot. Unbearably, uncomfortably warm.





	Miscalculation

Gaster furiously erased a line of text he had mistyped, glaring at the hand that had been a couple keys off as he was transcribing his notes. He exhaled, pulling himself back from the series of monitors before him, attempting to blink away the ache in his eye sockets. He absentmindedly took note of the clock, approximating that he had been at this for several hours already, and was still behind schedule. The work on the project was taking far longer than he had initially anticipated, and the documentation of S-1 and P-2 was incredibly tedious. It was eating away at his time voraciously.

He really needed to consider cutting down on the amount of detail in his notation if he were to have any hope of finishing this soon, without any assistance from his normal technicians. But the lack of detail could cause a loss of context that could be detrimental in later phases. Gaster didn't think it was something he could afford to do, with a project as precious as this one. There was no easy solution. His eyes  _ached_.

 _God_ , sometimes he really wished he had some kind of help with this.

(No one could know. No one could ever know. He discarded the idea as quickly as he had thought it.)

He attempted to rolling the aches and kinks out of his bones, but winced at the motion. How long had it been since he'd slept on an actual bed, he wondered.

Surely... not  _that_ long ago.

He absentmindedly reached over to retrieve more documents, but was met with protest at the movement. His form  _ached_ , and he realized perhaps he did require a break. Even a monster with his sort of stats, and a lot of coffee, needed to rest.

At least once ever couple months, surely.

Gaster stared at the screens before him with trepidation before putting them to sleep with a command prompt. He stretched his legs and looked at the remaining screens that were operational. His pet project.

Both of his subjects were sitting on the bed he's provided. S-1 seemed to be dozing softly, as 2-P was tinkering with the puzzle cube. Surely, nothing would go terribly wrong if he was gone  _one night_? Half of it was already gone, he amended.

He did not anticipate any more serious changes until the next batch of tests regardless.

Gaster found himself getting up from his computer chair, and gathering his things. A walk and a cigarette sounded too divine to pass up at the moment. Some sleep would do him good as well. It could very well make his next few days more efficient, and make up for lost time.

That's at least what he told himself to shake off the feeling of unease as he left the basement. As he left his two subjects alone.

Surely, they would be fine.

 

* * *

 

 

2-P made a noise of discontent, leaning further on his brother's side, reveling in the feeling of cool bones against his own. He felt hot. Unbearably, uncomfortably warm.

1-S's sleep was disturbed by the motion. He blinked up dazedly at his brother, murmuring softly. "you alright there, bro?"

Something about 1-S's concerned, warm eye lights made something in his stomach curl tightly and his form shiver despite the temperature. "Just  _hot_ ," he groaned. The taller skeleton took the opportunity to press more of his form against his brother, wrapping around him softly.

"you  _are_ hot, geez." 1-S pressed his phalanges against his skull, only to earn a moan in what seemed to be relief. He felt  _so warm_. "anything else the matter?" He asked, his eye lights flickering over his brother's form in visible worry.

Subject 2-P shook his head softly. He felt his face settling into a concerned grimace, despite himself. "i can't imagine you're getting sick, but..." there was palpable worry in 1-S's voice. "i don't want to grab  _him_  but-" there was clear distaste in his voice at the thought. "-if i have to i will." He promised, something in him determined.

2-P felt nothing but affection at his brother's sentiment.

"It's fine, brother." He assured S-1, before he visibly shuddered as another wave of heat ran through him. "Just... nn..." The taller skeleton wrapped himself more firmly around the other, trying to achieve more surface area. 2-P nuzzled into his brother's skull, reveling in their touch.

He needed to be  _closer_.

Subject S seemingly surrendered himself, allowing 2-P to adjust him and cling to him as needed. He ended up like an over-sized teddy bear on his brother's lap, with the other curled around him. 2-P continued to seek relief from him, rubbing against him to try to relieve some of the scorching heat.

"is it getting worse?" Subject S inquired after a while. His brother made a whine in reply, adjusting their position as if on cue. His breaths were becoming labored, shuddering things. "M-my... My magic..." He complained after a moment, sounding concerned.

And 1-S understood, seeing the soft glow of orange coming from his brother's joints. He had never seen that from either of the brothers before. Their caretaker hadn't demonstrated it either.

He had no clue what that was about, but it couldn't be a sign of whatever afflicted 2-P getting better.

"i think i should go grab  _him_ ," 1-S told him reluctantly.

His brother's only reply was his increasingly uneven breaths. He tried to escape the tangle of limbs he was trapped in, but the grip on him only tightened. Subject S saw the dim orange light of his brother's eyes through the darkness, actively revealing his distress.

"hey... c'mon..." 1-S tried to coerce him, gently. "he'll have a way to cool you down. just let me-"

" _ **Stay**_ **.** " 2-P protested sharply, his arms tightening around the other even further to a painful vice. Magic buzzed in the air, threateningly at his brother's proclamation. S-1 didn't dare move, frozen in something like fear, and only fractionally relaxing when his brother nuzzled against his neck once more. His captor seemed to let out a relieved sigh when 1-S didn't struggle, his hold marginally loosening. Just enough so it felt like he could breathe.

The shorter skeleton exhaled in something like relief.

Before 1-S could muster up the courage to try again, long phalanges pulled at his mandible, guiding his skull to the right. He blinked at the motion, before he met his brother's vivid eyes, and their mouths were pressed together with a low clink. There was a shock of magic at the touch, light but startling to 1-S's senses. His brother's skull felt warm against his own.

He felt the lingering magic tingle against his mouth. He felt like he had read about something like this before. The... kiss...? wasn't unpleasant, just surprising.

Before he felt the need to rip himself away, 2-P pulled back, his breathing still harsh. His forehead pressed against 1-S's own, " _Please_..." There was desperation in his expression, and he whined as he  _begged_. "I need... _I need_ \- I don't..." 2-P seemed confused, like he didn't know what he was begging for.

1-S didn't know either, but was determined to help him if he could. Whatever this was, if 1-S didn't need their  _caretaker_ to fix it then he would gladly do everything he could to solve it himself.

"anything you need," he told him sincerely.

He felt his sibling shudder in reply.

It was as though those words flicked some sort of switch, and his brother leaned back in, their magic sparking against each other. He was met with the press of a conjured tongue against his mandible, and he found himself opening his mouth for the other. It pressed inside his jaw, hot and tingling, and he found himself conjuring his own without really thinking about it.

The press of magic together felt  _nice_ , and made him feel fuzzy. They should have done this before, definitely.

1-S found himself gripping onto the threadbare gown the other wore, seeking some sort of way to make their position a little easier. He eventually found his hand brushing against his brother's spine, earning a breathy, pleased sigh in reply. He made an effort to pull a repeat performance, fingers ghosting against the other's spine drawing more soft sounds from him.

His mouth felt  _hot_. S-1 suddenly wondered how wise it was to be so close to his brother when he seemed afflicted like this. He wasn't entirely sure if it was contagious or safe to be around him - though really, it didn't matter. His brother  _needed_ him.

He wouldn't abandon him. Never.

His thoughts were scattered by the feeling of 2-P's nimble fingers stroking his ribs through the fabric of his gown. Another hand found purchase on his shoulder, his grip tight. It felt almost as though the other thought 1-S would vanish if he loosened it even slightly. Despite the low pulse of pain from his shoulder it felt  _nice_ , and his exhale caught into a whimper.

"Brother..." 2-P breathed. 1-S felt warm in more ways than one.

It was then, when 1-S was trying to find a more comfortable position (yet something closer _closer_ _ **closer**_ he needed to be  _closer_ ) that he felt something warm and soft brush against his legs. He found himself pausing in his ministrations, to look and catch the low orange glow coming from his brother's pelvis. A magical construct, something fleshy much like their tongues had manifested.

He wasn't sure what is was for, and yet the sight of it fanned the flames of the fire that was trying to consume him. He didn't hesitate to pull a preoccupied hand away from his ministrations to investigate. A displeased noise tore from his brother's maw, something sounding distressed, that was quickly silenced as he ran his hand across the manifestation. 2-P shuddered in his touch.

"bro...?" He found himself murmuring. "are you alr-"

" _More_ ," 2-P broke out sharply, cutting him off. "Touch me,  _please please please- I need... "_  He broke off with a bone rattling shudder.  _"_ So _warm..."_ His voice was dripping in desperation.

Something caught in his rib cage at the words, and he felt the fire beneath his bones go from a smoldering camp fire, to something raging and untamed. He couldn't think straight. It didn't matter. His brother needed him.

2-P was  _his_  and needed him. Needed to be  _helped_ marked _claimed_.

1-S continued in his ministrations, softly tracing the ecto-flesh beneath his fingertips until he found the areas that made 2-P grip onto him more tightly. The spots made him sigh and whine for  _more._

Tentatively, he pulled away from 2-P briefly. The other seemed distraught at the loss, but trembled as he brought his tongue to the organ presented. The reaction of swiping his tongue across the bundle of sensitive flesh that he had been prying at earlier was pleasant to his ears. 2-P's femurs trembled at the action, and he continued until his brother was a dripping mess, his fevered begging nearly a constant sound.

He ceased when the weight of his own magic, coagulating in his pelvis drew his attention. It had formed on its own, though 1-S knew he couldn't manage to use his magic  _at all_ in this state. His mind felt too fuzzy, to scattered by his body's rising temperature and the incessant need to crawl under 2-P's bones. He was met with a long, thick and sensitive ecto-organ. It was different to the one that his brother had, the other looking almost flower like in comparison. Something in him was drawn to it.

He didn't hesitate to brush the two together, to slide his cock against the orange flesh to provoke a reaction. It felt  _good_ and the fire in his SOUL burned brighter. He grinded the two together softly, reveling in the sensation. It drew out soft-moans and needy whines from the both of them. It felt  _good_.

"So  _hot_ ," 2-P moaned. " _More, please_ brother _..._ I  _cant..."_

He  _knew_ what to do next, despite himself. Something inside him already knew, as he aligned his cock against the dripping folds of his brother's dripping entrance. He teased softly, rubbing back and forth against the slit, drawing wanton moans from the other until he slipped in  _further_.

It felt warm and hot and  _electrifying_ in ways that weren't comprehensive to 1-S, and it took the few remaining shreds of willpower to not move deeper at the distressed warble his brother gave at the intrusion.

He could see his brother's bright eye lights, their color bleeding onto the white walls of their room. The warm, cascading glow of orange against blue pleased him in some deep, indescribable way. It was in the very same way that seeing his brother's disheveled, pleading form did.

"Ah, please-" his brother broke out after a moment, startling him out of his hazy retrospection. " _move... please... ngh."_ At those words all the control 1-S had shattered completely. His SOUL burned like fire and he rocked into the other, sloppily and quickly.

 _"Harder,_ " his brother cried. It felt  _good_ , so terribly good, and the way his brother responded only spurred him on further until he felt like he was going to  _burst._ Until his SOUL felt like liquid magma _._

He drank in 2-P's expressions and sounds greedily, enjoying the way he was coming undone. The low gasps and pleas when he rocked into him at just the right spot, the way he was begging for  _moremore_ _ **more**_ was beautiful. He needed more.

"such a good mate," he found himself murmuring breathlessly and he continued to thrust roughly into his brother's tight cunt, reveling in how good it felt. 2-P whimpered at his words, his walls fluttering around him in response, and he angled to bare his throat in reply.

1-S didn't think the fire, the need in him could get any bigger but it did. He found himself pounding furiously into the other, his teeth finding purchase on his offered bones and biting into them. His brother cried out in pleasure, and 1-S could feel the tightness around his cock clenching down tightly. It pushed him over the edge, and he couldn't contain the groan that left his mouth. He rode out the climax furiously, his magic pouring into the other. His brother babbled sweet nothings as he did so, his form trembling lightly.

And it was like the flames were doused after that moment, overridden with the low, heady bliss that enveloped him. His brother seemed to be in a similar state, and his pulled himself away, readjusting to cuddle with his sibling. The position was familiar, comforting even. He heard a distant, rumbling sound, but dismissed it in favor of curling closer to his brother who seemed to be in a similar state.

"you alright?" he asked softly. 2-P made a affirmative hum in favor of speaking as he nuzzled into his ribs. He released a breath he didn't know he had been holding, relieved he hadn't hurt his brother somehow. He let the haze and bliss settle over him, and the two fell into a comfortable, sleepy silence for a moment.

2-P was the one to break it.

"You're... Making a weird sound..." His brother told him, weakly laughing. He smiled at the sound, despite taking a moment to listen to himself, bemused.

"am i?" He murmured into 2-P's shoulder, relishing in the contact. He still ached to be  _close_ close _ **closer**_ **.**

Subject S shuddered. Their ecto-organs hadn't dissipated, and his ached, wanting attention. He struggled not to grind into the other, and simply hold him. But a part of him still  _needed-_

"Yeah. You're rumbling... It's nice..." His brother's voice roughly cut off his thoughts. He blinked, before touching his chest and realizing that his sibling was correct. He made a thoughtful sound at the discovery, but his attention was drawn back to 2-P.

His bones still glowed with magic, cascading his features in warm light. 1-S found himself still somewhat hazy, the embers of the heat from before still burning lowly. He could feel the heat from his brother's bones. Not as vicious and scorching and before, but a dull, rising warmth.

"mm...you want... more?" He found himself asking after a long, hesitant pause. He stole a side glance at his sibling's expression, taking in the desire that bled into his eye lights at the question. Taking in the dusting of orange magic on his zygomatic process.

"...Please." He croaked after a moment, a touch of embarrassment visible.

Something like anxiety uncurled in his gut at the permission. "it's okay. i'll take care of you." He promised, rubbing at his scapula soothingly. "i wouldn't hurt you." Something about that statement made 2-P sink further into him, relaxed.

"I know."

**Author's Note:**

> i initally intended to do a lot more with this, like having gaster come back and sans flip out and be really agressive and protective and feral and mating bond shit but god i cant write lmao
> 
> also having to write them as 2-p and 1-s respectively was a fucking nightmare give them names gaster


End file.
